1. Field of the Invention
The present invention relates to a method of detecting the junction of a lesion and a wall, such as a lung nodule attached to pleura or a polyp attached to a colon wall, in an image scanned from a human or animal body, particularly but not exclusively in a computed tomography (CT) image. The invention encompasses software and apparatus for carrying out the method.
2. Background Art
Detection of suspicious lesions in the early stages of cancer can be considered the most effective way to improve survival. Lung nodule detection and polyp detection are some of the more challenging tasks in medical imaging.
Computer-assisted techniques have been proposed to identify regions of interest containing a nodule in a CT scan image, to segment the nodule from surrounding objects such as blood vessels or the lung wall, to calculate physical characteristics of the nodule, and/or to provide an automated diagnosis of the nodule, to provide some examples. Fully automated techniques perform all of these steps without intervention by a radiologist, but one or more of these steps may require input from the radiologist, in which case the method may be described as semi-automated.
Detection of the size or extent of a lesion is important for accurate diagnosis, but it is difficult to detect the extent of a lung nodule attached to the pleura, or to separate a nodule from the pleura, because of their similar intensity in CT scans. Likewise, it is difficult to detect the boundary between a polyp and the colon wall.
Patent publications US-A-2003/0099384 to Zeng et al., filed Sep. 30, 2002, and US-A-2003/0099389 to Zeng et al., filed Nov. 23, 2001, describe methods of detecting pleural nodules using morphological closing for small nodules, and a deformable surface model for nodules larger than the structural element used for morphological closing.
Patent publication WO 03/010102 and the article ‘Lung Nodule Detection on Thoracic Computed Tomography Images: Preliminary Evaluation of a Computer-aided Diagnostic System’, Gurcan M et. al., Med. Phys. 29 (11), November 2002, pp. 2552-2558, describe a method of detecting pleural nodules using a local indentation search next to the lung pleura by finding a pair of points on a closed contour along the boundary of the lung where the ratio of the distance between the points along the boundary is greater than the straight line distance between the two points by more than a predetermined threshold.